Lubricants for steam turbines



Patented Aug. 28, 1951 LUBRICANTS FOR STEAM TURBINES Robert G. Mastin, Okmulgee, Qklgn, assignor to Cities Service Oil Company, Bartlesville, Okla., a corporation of Delaware No Drawing. Application July 13, 1948, Serial No. 38,549

2 Claims.

My invention relates to improvements in steam turbine lubricants and more particularly to lubricants protected against oxidation by having incorporated therein an antioxidant comprising certain substituted metatoluidines.

It is important that a steam turbine lubricating oil be resistant to oxidation, since the oils are used under extreme pressures of heat and friction, and it is important that a minimum of gum formation take place in the oil under conditions of operation.

It is an object of my invention to provide an antioxidant for lubricating oils, which, when added to the oil in relatively minor quantities, will inhibit oxidation of the oil over relatively long periods of time.

It is a further object of my invention to provide an improved lubricant for turbines which \i' illremain e'fficieht for relatively long periods of time under extreme operating conditions.

I have discovered a number of extremely e'fiecti've antioxidants for steam turbine oils, even when used in very small percentages. Petroleum turbine oil stocks, refined and prepared especially for the lubrication of steam turbines, have relatively short induction periods unless they are suitably protected against oxidation. Uninhibited stocks of this type, in genera-Leven though re fined to a high degree, stand up a relatively short time when tested by 'S. T. M. Method of Test for Determining the Oxidation Characteristics of Inhibited Steam Turbine Oils D943-47T.

In accordance with the features of my invention, the improved lubricating oil composition is comprised essentially of a refined petroleum lubricating oil stock of suitable physical characteristics for use as a steam turbine lubricant, and containing an extremely small portion of certain substituted metatoluidines. It has been found that these substances when incorporated in a turbine oil will inhibit the oxidation process and will extend the useful life ofthe oil far beyond that normally given when no antioxidizing material is present.

The antioxidizing compounds are best illustrated by the graphic formula:

where R represents a radical selected from the group consisting of phenyl, tolyl, xylyl, mesityl, naphthyl, cumenyl, cymenyl, and anisyl. Chemical terms ordinarily applied to the above compounds that have been found to be efiective antioxidants are:

l. Benzyl-m-toluidine 2. Methyl benzyl-m-toluidine 3a. 2,3-dimethyl benzyl-in-toluidine 3b. 2,4adimethyl benzyl-m-toluidine 3c. 2,5-diniethyl benzyl-mtoluidine 2,4,G-trimethyl benzyl-m-toluidine Naphthyl methyl-m-toluidine Cumene methyl-m-toluidine Cymene methyl-m-toluidine plviethoxy benzy1mtoluidine.

Metatoluidine is used as the starting material for condensing with the aromatic hydrocarbons which previously have been chloromethylated.

The general reaction involved in the preparation of these materials is a reaction between metatoluidine and the chloromethyl'ated hydrocarbon whereby the hydrocarbon is substituted for one of the hydrogen atoms of the amine radical of the metatoluidine, hydrogen chloride being split out in the process.

A typical example of the preparation of a chloromethylated hydrocarbon is that of Blane (Bull. Soc. Chim. (a) 33, 313 (1923) in which a mixture of 600 grams of benzene, grams paraformaldehyde and'60 grams zinc chloride are heated to 60 C. with stirring. A steam of hydrogen chloride is passed into the mixture until no more gas is absorbed. Washing and purification yields benzyl chloride.

In order that those skilled in the art may more fully understand the manner of preparing my new antioxidants the following examples are given. However, these examples should not be construed to limit my antioxidants to the particular lcompounds indicated in the examples since other similar compounds prepared in a similar fashion may serve equally well as antioxidants, as indicated above.

EXAMPLE 1 washed twice with water, dried, and subjected to vacuum distillation. After removal of the excess metatoluidine, a yield of grams of 2-5-dimethyl benzyl metatoluidine was obtained. This substance was a clear liquid boiling at 222 to 225 C. at 16mm. of mercury.

3 EXAMPLE 2 Four hundred twenty-eight grams of metatoluidine together with 105 grams of sodium bicarbonate previously made into paste with 100 mls. of water were mixed in a flask; the flask was then heated until the temperature reached 90 to 95 C. and stirring was started. 176 grams of naphthalene methyl chloride was then added dropwise to the reacting mixture over a period of about one hour. The mixture was then heated for an additional three hours. The contents of the flask were then washed twice with water, dried, and subjected to vacuum distillation. After the excess metatoluidine had been removed, a yield of 185 grams of naphthyl methyl-metatoluidine Was recovered. This substance is an amber viscous syrupy liquid boiling at 245 to 247 C. under a vacuum of 13 mm. of mercury absolute.

I have found that sodium carbonate may also be used in place of sodium bicarbonate as an acid fixer, although sodium bicarbonate is preferably used on account of its high purity and convenience in handling. It has been found that reagents of. stronger basicity increase the proportion of higher boiling by-produots formed in the reaction, thus cutting down on the yield of the desired product.

It is also desirable to use an excess of metatoluidine, since when molar equivalent amounts are used, the product tends to react further with the chloromethylated hydrocarbon to form a tertiary amine. However, when a large excess of metatoluidine is used, formation of the tertiary amine is inhibited, and a large yield of the desired secondary amine is produced. The tertiary amine formed by the reaction of equimolar quantities of metatoluidine and chloromethylated hydrocarbons has been tested as a turbine oil antioxidant but has been found unsatisfactory for this purpose.

Concentrations ranging from 0.1 per cent to 1.0 per cent of the substituted metatoluidines described above have been found effective in prolonging the life of a turbine oil. Table 1 shows the effectiveness of the proposed antioxidant in two turbine oils of diiferent origin. Blanks indicate that no tests were made for the particular compounds or concentrations.

Table 1 Induction Hours Oil A Oil B Blank Oil Benzyl-m-toluidine:

0.50% Cumene methyl-m-toluidine:

0.50% Oymcne methyl-m-toluidine: 0.5 p-Methyoxy benzyl-m-toluidine:

4 The physical properties of a turbine oil are changed very little by the addition of 0.35% of the various toluidines. Table No. 2 presents the data resulting from these physical tests.

Table No. 2

Turbine Oil plus Methyl Benzyl-m- Blank on toluidine g l f 035,7 o m me Acid Number 0.025 0.025 0.025 Color, N. P. A 2- 2 2- Flash point, "F l. 410 405 400 Fire point, "F 455 455 450 Gravity, A. P. I 30.4 30. 5 30. 6 Pour point, F. l5 l5 15 Steam Emulsion N 38 43 42 Viscosity F 152. 4 154. 6 156. 0

Turbine Oil plus 2,5-Di- 2,4,6- methyl Trimethyl g i benzyl-m benzyl-m toluidine toluidine 0.35% 0.35% 0 Acid Number 0. 025 0. 025 0. 025 Color, N. P. A 2- 2 2- Flash point, F 400 410 400 Fire point, F. 450 455 450 Gravity, A. P. I 30. 5 30. 5 30. 5 Pour point, "F 15 15 15 Steam Emulsion No 41 45 47 Viscosity 100 F 152. 8 152.8 155. 1

ROBERT G. MASTIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,790,794 Calcott Feb. 3, 1931 2,009,480 Craig July 30,1935 2,257,869 Trautman Oct. '7, '1941 2,308,282 Howland Jan. 12, 1943 FOREIGN PATENTS Number Country Date 364,092 Great Britain Dec. 23, 1931 

1. A LUBRICANT COMPRISING A MAJOR PROPORTION OF A MINERAL OIL OF LUBRICATING VISCOSITY, AND A MINOR PROPORTION, SUFFICIENT TO IMPROVE THE PROPERTIES OF THE OIL, AS REGARDS OXIDATION, OF P-METHOXY-BENZYL-M-TOLUIDINE. 